I have looked all over and I still can't find an example of how to create two shifted columns in a Pandas Dataframe within its groups.
I have done it with one column as follows:
data_frame['previous_category'] = data_frame.groupby('id')['category'].shift()
But I have to do it with 2 columns, shifting one upwards and the other downwards.
Any ideas?
It is possible by custom function with GroupBy.apply
, because one column need shift down and second shift up:
df = pd.DataFrame({
'B':[4,5,4,5,5,4],
'C':[7,8,9,4,2,3],
'F':list('aaabbb')
})
def f(x):
x['B'] = x['B'].shift()
x['C'] = x['C'].shift(-1)
return x
df = df.groupby('F').apply(f)
print (df)
B C F
0 NaN 8.0 a
1 4.0 9.0 a
2 5.0 NaN a
3 NaN 2.0 b
4 5.0 3.0 b
5 5.0 NaN b
If want shift same way only specify all columns in lists:
df[['B','C']] = df.groupby('F')['B','C'].shift()
print (df)
B C F
0 NaN NaN a
1 4.0 7.0 a
2 5.0 8.0 a
3 NaN NaN b
4 5.0 4.0 b
5 5.0 2.0 b
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